Microwave-Assisted Production and Regeneration of Granular Expanded Graphite for the Adsorption of Cationic Dye Methylene Blue from Aqueous Solutions.

This study investigated the use of microwave (MW) to enhance the performance of a granular thermo-plasma expanded graphite (GTPEG) to remove an organic cationic dye, methylene blue (MB), from freshwater, taking the benefits of MW-assisted regeneration. Expanded graphite (EG), low-density and mesoporous, has been proposed previously as a means of extracting organic compounds from water due to its hydrophobicity and weak polarity. We granularized EG to facilitate its subsequent regeneration and reuse and separation, and MW was used to improve the adsorption of EG. The most important factors affecting adsorption were determined using response surface methodology, along with 3-D graphics illustrating the relationship between several variables. The experimental results show that 94% of MB adsorbed onto MW-GTPEG in deionized distilled water within 20 min. Additionally, adsorbent regeneration using MW did not affect the adsorption capacity and rate after 10 cycles albeit with a small weight loss of <8%. From our results, we believe that the main factor affecting the adsorption was the physical characteristics of the adsorbent, with other minor factors such as the adsorbent dose and initial concentration. Our findings suggest that MW irradiation may be a promising alternative for enhancing and regenerating GTPEG.